Method of refinement of microstructure of metallic materials

ABSTRACT

The present invention provides a method for refining microstructure of metallic materials and the present invention relates to a method in which cavitation (cavities) is formed in molten metal by the application of high-energy vibrating force to a metal in the process of solidification, and the newly formed solid crystal particles are crushed by the impact pressure generated during the collapse of the cavities to refine the microstructure of the material, and high-energy electromagnetic vibrating force is applied to a solidifying metal sample  10  by the simultaneous imposition of an electric current and a magnetic field in an apparatus comprising an electromagnet  12  for applying a stationary magnetic field and an electrode  11  for passing an alternating current through the metal sample, so that the solid crystal particles are crushed into small pieces, yielding a fine microstructure thereof.

DESCRIPTION OF THE INVENTION

This invention relates to a method for refining a microstructure ofmetallic materials. More particularly, the present invention relates toa method of refinement of microstructure of metallic materialscharacterized in that allows microstructure of metallic materials to berefined irrespective of the type of metal or refining agent, whereinhigh-energy vibration force such as electromagnetic vibrating force,ultrasonic vibrating force, or the like is applied directly to moltenmetallic materials. The present invention also relates to a method forrefining solid metal particles by the above-described method to movethem to a prescribed location.

BACKGROUND OF THE INVENTION

Methods for refining microstructure of metallic materials are broadlyclassified into two types such that methods in which refining agents areadded to molten metallic materials to refine the microstructure of themetallic materials solidified, and methods in which the solid metallicmaterials are subjected to forming processes and heat treatments torefine the microstructure thereof.

Specifically, in the first group of the methods, refining agents act asnuclei for the solid metal crystal particles to be formed duringsolidification, yielding a refined microstructure that corresponds tothe dispersion state of the refining agents, whereas in the second groupof the methods, microstructures refined are obtained byrecrystallization of the metals generated by heat treatments that followforming processes such as rolling, extrusion, or the like.

In the methods of the first group, however, a close crystallographicrelationship achieved between the refining agent and the solid-crystalparticles is required in order to allow the refining agent to beeffective, and it is impossible to obtain adequate refining agents forsome types of metals.

In addition, the refined structure smaller than the particle size of therefining agent cannot be made.

In the methods of the second group, it is difficult to yield adequaterefining because forming processes such as rolling, extrusion and thelike are limited in their effects, and exceeding these limits causesfracture of the metal, and there is a tendency to cause metalsrecrystallized as well as metal particles enlarged as a result of theheat treatment that follows forming.

An urgent need therefore existed for developing a novel method forrefining microstructure of metallic materials that would be able tosolve the above-described problems of the conventional methods.

An objective of the present invention is to overcome these subjects.

ABSTRACT OF THE INVENTION

The present invention provides a method for refining microstructure ofmetallic materials.

The present invention relates to a method which comprises formingcavitation (cavities) in molten metal by the application of high-energyvibrating force to a metal in the process of solidification, andcrushing the newly formed solid crystal particles by the impact pressuregenerated during the collapse of the cavities to refine themicrostructure of the material. High-energy electromagnetic vibratingforce is applied to a solidifying metal sample 10 by the simultaneousimposition of an electric current and a magnetic-field in an apparatuscomprising an electromagnet 12 for applying a stationary magnetic fieldand an electrode 11 for passing an alternating current through the metalsample, so that the solid crystal particles are crushed into smallpieces, yielding a fine microstructure thereof.

DETAILED DESCRIPTION OF THE INVENTION

Specifically, an objective of the present invention is to provide anovel method for refining microstructure of metallic materials thatcapable of refining the microstructure thereof irrespective of the typeor composition of the metallic materials.

Another objective of the present invention is to provide a method forrefining microstructure of metallic materials that facilitates refiningeven for metals that have been difficult to refine in the past.

Still another objective of the present invention is to provide a methodfor refining microstructure of metallic materials to move it to aprescribed location.

The following technological means are employed in the present invention,which is aimed at overcoming the aforementioned subjects.

(1) A method for refining microstructure of metallic materials,characterized in that comprises forming cavitation (cavities) in moltenmetal by the direct application of high-energy vibrating force such aselectromagnetic vibrating force, ultrasonic vibrating force to themolten metal, crushing the resulting solid metal crystal particles intosmall pieces by the impact pressure generated during the collapse of thecavities, and yielding a refined microstructure thereof.

(2) The method for refining microstructure of metallic materialsaccording to (1) above, wherein the high-energy vibrating force isapplied during the solidification of said metal.

(3) The method for refining microstructure of metallic materialsaccording to (1) or (2) above, wherein the high-energy vibrating forceis applied to a metal in the process of solidification by thesimultaneous imposition of an electric current and a magnetic field tosaid molten metal or solidifying metal.

(4) A method for refining microstructure of metallic materials,characterized in that comprises forming cavitation (cavities) in moltenmetal by the direct application of high-energy vibrating force such aselectromagnetic vibrating force, ultrasonic vibrating force to themolten metal, crushing solid particles of other metals, intermetalliccompounds, or the like dispersed in the molten metal as well as thesolid metal formed during solidification into small pieces by the impactpressure generated during the collapse of the cavities, and yieldingrefined microstructure thereof.

(5) A method for refining microstructure of metallic materials,characterized in that comprises forming cavitation (cavities) in moltenmetal by the direct application of high-energy vibrating force such aselectromagnetic vibrating force, ultrasonic vibrating force to themolten metal, crushing the solid particulate ceramics or other nonmetalsdispersed in the molten metal as well as the solid metal formed duringsolidification into small pieces by the impact pressure generated duringthe collapse of the cavities, and yielding refined microstructurethereof.

(6) A method for refining solid metal particles formed duringsolidification to move them to a prescribed location by the simultaneousimposition of an electric current and a magnetic field on the moltenmetal in the process of final solidification.

(7) The method according to (6) above, wherein the solid metal particlesformed during solidification are refined to shift them to a periphery ofa tube by the simultaneous imposition of an electric current and amagnetic field on the molten metal in the process of finalsolidification.

(8) The method according to (6) above, wherein the solid particles ofother metals, intermetallic compounds, or the like dispersed in moltenmetal as well as solid metal particles formed during solidification arerefined to shift them to a periphery of a tube by the simultaneousimposition of an electric current and a magnetic field on the moltenmetal in the process of final solidification.

(9) The method according to (6) above, wherein the solid particulateceramics or other nonmetals dispersed in molten metal as well as solidmetal particles formed during solidification are refined to shift themto a periphery of a tube by the simultaneous imposition of an electriccurrent and a magnetic field on the molten metal in the process of finalsolidification.

(10) The method according to (6) above, wherein the solid particlesdispersed in molten metal are refined to move them to a locationseparated from the location of the initial dispersed state by thesimultaneous imposition of an electric current and a magnetic field.

The present invention will now be described in detail.

The invention of this application is characterized in that themicrostructure of metallic materials is refined by the directapplication of high-energy vibrating force to them. In this case, it isimportant that electric current and magnetic field be simultaneouslyapplied as the high-energy vibrating force, whereas applying theelectric current or magnetic field alone has no significant effect onthe fine microstructure of metallic materials. The reason is that theelectromagnetic vibrating force is a Lorentz force that can only begenerated when an electric current and a magnetic field are appliedsimultaneously.

Electromagnetic vibrating force and ultrasonic vibrating force areexemplified as specific examples of high-energy vibrating force, butthese examples are not all-encompassing and include all other types offorce capable of exerting high-energy vibrating force on molten metal inthe same manner.

The high-energy vibrating force is applied to molten metal, in whichcase it is preferable for the high-energy vibrating force to be appliedto solidifying metal.

As used herein, the term “molten metal” refers to a metal that iscompletely liquefied which kept at a temperature above its meltingpoint. In addition, the term “solidifying metal” refers to a liquidmetal containing solid metal crystals that form at a temperature belowthe melting point.

The present invention can be adequately applied, for example, toaluminum alloys such as Al—Si alloys or magnesium alloys, but adistinctive feature of the present invention is that it allows anyrefining agent or metal to be used, and that, in particular, there is nodependence on the type or composition of metal.

When high-energy vibrating force is applied to a solidifying metal inaccordance with the above-described method, the microstructure thereofis refined by forming cavitation (cavities) in the molten metal andallowing the impact pressure generated during the collapse of thecavities to crush the resulting solid metal crystal particles into smallpieces.

Because cavitation is induced while some of the metal is still in themolten state, not only the newly formed solid metal crystals but alsothe already existing solid metal particles are crushed by theapplication of high-energy vibrating force until the molten metal hascompletely solidified, making it possible to obtain a refinedmicrostructure thereof.

A solidified microstructure of metallic materials can therefore berefined as well.

The high-energy vibrating force should be applied during (in the processof) solidification. It is difficult to form cavitation (cavities) whenhigh-energy vibrating force is applied to metallic materials aftersolidification thereof, and therefore there is a possibility that thesolid metal crystal particles will not be crushed.

In addition, in this invention, even metals that are difficult to refineby conventional methods can be readily refined because the refiningeffect of this invention by the high-energy vibrating force does notdepend on the type or composition of the metal.

Silicon crystals as initially crystallized particles in a hypereutecticaluminum-silicon alloy, can, for example, be refined to a crystalparticle diameter of 0.5-3.0 μm by the method for refiningmicrostructure of metallic materials through application of high-energyvibrating force in accordance with the present invention.

The present invention also allows solid particles of other metals,intermetallic compounds, or the like, as well as solid particulateceramics or other nonmetals dispersed in molten metal to be crushed inthe same manner as the solid metal formed during solidification

The method of the present invention allows, for example, 20- to 30-μmsilicon carbide particles dispersed in an aluminum alloy to be refinedto a size of 0.1-2.0 μm.

Another feature of the present invention is that the solid metalparticles formed during solidification can be refined to move them to aprescribed location by the simultaneous application of electric currentand magnetic field to the molten metal in the process of finalsolidification thereof. Specifically, the solid metal formed duringsolidification can be refined to shift it to the periphery of acylindrical tube or container disposed such that the axial direction ofthe cylinder is orthogonal to the magnetic field; solid particles ofother metals, intermetallic compounds, or the like, as well as solidparticulate ceramics or other nonmetals dispersed in molten metal can beshifted in the same manner as the solid metal formed duringsolidification to the periphery of a cylindrical tube or containerdisposed in the same manner as the solid metal; and the aforementionedsolid particles can be refined to move them to a separate location theinside tube or container from the location of the initial dispersedstate. Another specific feature is that the shifting locations can beconcentrated in the end portion of a sample by moving the sample withinthe magnetic field.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an example of an apparatussuitable for implementing the present invention.

DESCRIPTION OF MARKS

-   10 metal sample-   11 electrode-   12 electromagnetic coil

EXAMPLES

The present invention will now be described in detail through examplesthereof, but the present invention is not limited by these examples.

FIG. 1 shows an example of the apparatus for implementing the presentinvention. In the drawing, 10 is a metal sample, 11 is an electrodedisposed in contact therewith, and 12 is an electromagnetic coildisposed such that it envelops the metal sample.

When an alternating current of about 80 A is passed through the metalsample via the electrode, the metal sample is melted by Joule heatgenerated, and the temperature of the metal sample reaches a prescribedtemperature. The temperature of the molten metal sample is then loweredand solidification of the metal sample is started by reducing theelectric current. An electromagnetic vibrating force based on thealternating current and a stationary magnetic field is created by theapplication of a stationary magnetic field of 1.4 T (Tesla) through theintermediary of the electromagnet 12, and at this time the molten metalsample is vibrated by the vibrations. As a result, cavities are formedin the metal sample, and the solidified metal crystals are crushed bythe cavitation phenomenon.

The above-described apparatus was used to impose electromagneticvibrating force upon a solidifying alloy in the form of a hypereutecticAl-17% Si alloy. The results are shown in Table 1. As shown in Table 1,it was found that the silicon particles initially crystallized werecrushed into small pieces. TABLE 1 Crystal grain diameter (μm) Exampleof present Introduction of high 0.5-3 invention vibrational energyConventional example Use of refining agents   30-50

Examples of the Inventions Defined in Claims 4-5

The above-described apparatus was used to apply electromagneticvibrating force to a solidifying aluminum alloy and to solidifying zincin order to refine silicon carbide particles dispersed in the aluminumalloy and to refine Fe₃P compound particles dispersed in the zinc. Theresults are shown in Table 2. It was found that the dispersed siliconcarbide particles and Fe₃P compound particles were crushed into smallpieces. TABLE 2 Diameter of Fe₃P Diameter of SiC particles particles inzinc (μm) in aluminum alloy (μm) Example of present 10-1 2-0.1 inventionConventional  50-100 20-30   dispersant

Examples of the Inventions Defined in Claims 6-10

Electromagnetic vibrating force was applied to an Al-17% Si alloy in theprocess of final solidification in order to refine the alloy. As aresult, the refined silicon particles as initially crystallized in auniformly dispersed sample could be moved to the surface of thesurrounding walls of a cylindrical tube.

In addition, an alloy obtained by dispersing Fe₃P particles in zinc, andan alloy obtained by dispersing SiC particles in an aluminum alloy couldalso be moved to the surface of the surrounding walls of the cylindricaltube in the same manner as in the case of the Al-17% Si alloy.

Examples of the present invention have been described in detail above,but these examples merely serve as an illustration, and the same effectcan be achieved for other metals, alloys, intermetallic compounds,semimetals, nonmetals, and the like. The present invention allowsembodiments incorporating various changes based on the knowledgepossessed by those skilled in the art to be implemented as long as thesechanges remain within the scope of the present invention.

The present invention relates to a method for refining microstructure ofmetallic materials characterized in that comprises forming cavitation(cavities) in molten metal by the direct application of high-energyvibrating force such as electromagnetic vibrating force, ultrasonicvibrating force to the molten metal, and crushing the resulting solidmetal crystal particles into small pieces by the impact pressuregenerated during the collapse of the cavities, and yielding a refinedmicrostructure of the metal. The present invention allows microstructureof metallic materials to be readily refined to the level of fineparticles without the use of refining agents and without any relation tothe type or composition of the metal. It is also possible to refinesolid particles of other metals, intermetallic compounds, or the likedispersed in the molten metal. It is further possible to shift solidmetal particles and solid particles dispersed in molten metal toward theperiphery of a tube or container.

1-14. (canceled)
 15. A method for shifting a refined microstructure of ametallic material, comprising: solidifying a molten metallic material attemperatures lower than a liquidus of the molten metallic material; andvibrating the solidifying molten metallic material by applying analternating electric current and a magnetic field simultaneously at acurrent value and a Tesla value configured to crush solid crystalparticles of the solidifying metallic material into small pieces; andshifting the small pieces to a periphery of a cylindrical tube orcontainer with said alternating current and said magnetic field set at acurrent value and a Tesla value configured to concentrate said refinedmicrostructure of the metallic material in the periphery of thecylindrical tube or container. 16-17. (canceled)
 18. The method of claim15, wherein the applying further comprises applying the electric currentand the magnetic field during last stages of solidifying of thesolidifying metallic material.
 19. (canceled)
 20. The method of claim15, wherein the magnetic field is generated with an electromagnetic coilenveloping the metallic material.
 21. The method of claim 15, whereinsaid current value and said Tesla value configured to crush solidcrystal particles comprises: a current value less than a current valueused to melt said metallic material.
 22. The method of claim 15, whereinsaid current value and said Tesla value configured to concentrate saidrefined microstructure comprises: a Tesla value of 1.4 Tesla.
 23. Themethod of claim 15, wherein said metallic material is Al—Si alloy andsaid small pieces have a crystal grain diameter between 0.5 and 3 μm.24. The method of claim 15, wherein said metallic material is Al—Sialloy with silicon carbide particles dispersed therein and said smallpieces comprise small silicon carbide particles having a crystal graindiameter between 0.1 and 2 μm.
 25. The method of claim 15, furthercomprising: concentrating said metallic material in an end portion ofsaid metallic material by moving the metallic material within themagnetic field.